Abnormal vascular tone and reactivity is common in essential hypertension in the easily accessible vascular beds of the extremities. While abnormalities of renal perfusion can clearly cause hypertension, little is known about renal vascular reactivity in these patients. Sodium restriction and drugs influencing sodium balance are widely utilized in treatment. We have documented the effects of varying sodium intake on renal vascular reactivity in normal man and have preliminary data which indicate a striking abnormality of renal vascular reactivity to pharmacologic, reflex and emotional stimuli in essential and secondary hypertension. An optimal index of vascular reactivity is provided by the intra-arterial infusion of vasoactive agents, as the dose may be sufficiently small that complicating systemic effects do not occur. We utilize this route to administer graded doses of a number of vasoconstrictor and vasodilator agents to assess renal vascular responsiveness in normal subjects and patients with essential or secondary hypertension. Moreover, the use of specific antagonists to norepinephrine and angiotensin's vascular action provides insight into their role, respectively in maintaining the increase in renal vascular resistance and hypertension. The interpretation of the renal response to specific antagonists is strengthened by obtaining simultaneously an index of the state of activation of the relevant hormonal system - by measuring the arterial and renal venous plasma concentrations of renin, angiotensin II, norepinephrine and dopamine-beta-hydroxylase. We have already established normal values for each index. The studies will be done during clinically indicated selective renal arteriography and assessment will be made with the xenon washout method and the selective arteriogram. The objective is to define further the determinants of renal vascular tone and vascular reactivity in normal man, the character of variations from normal in patients with hypertension of diverse etiology and the relationship of these abnormalities to the state of the retin-antiotensin and sympathetic nervous systems. A second objective is to assess the diagnostic utility of Saralasin (P113) in identifying reno-vascular hypertension and of a new, oral converting enzyme inhibitor (SQ 14225) in therapy.